Interaction of Cr(diimine)(3)(3+) complexes with DNA

Luminescence spectroscopy coupled with capillary electrophoresis (CE) provi des insight into the nature and stereoselectivity of Cr(diimine)(3)(3+) int eractions with polynucleotides. Photoluminescence measurements on Cr(phen)( 3)(3+) and Cr(bpy)(3)(3+) in air or N-2-saturated solution demonstrate stro ng B-DNA quenching of Cr(diimine)(3)(3+) emission intensities and lifetimes . Both dynamic and static quenching are observed, the latter being attribut ed to DNA bound Cr(diimine)(3)(3+). Very rapid quenching is also observed w ith deoxyguanosine monophosphate (dGMP), while no bimolecular quenching is observed with other mononucleotides. Likewise, poly(dG-dC).poly(dG-dC) caus es rapid quenching, while only minor quenching is observed for poly(dA-dT). poly(dA-dT). These emission results are consistent with a DNA quenching mec hanism involving guanine base oxidation. The electropherogram resulting fro m the co-injection of rac-Cr(phen)(3)(3+) and rac-Ru(phen)(3)(2+) into a ca pillary containing B-DNA indicates a similar binding constant for the two c omplexes, while the enantiomeric stereoselectivities are reversed. CE studi es for Ru(phen)(3)(2+) with distamycin A (an AT selective minor groove bind er) reveal a significant reduction in complex migration times and a complet e loss of enantiomeric discrimination. These results are consistent with a literature model where nonelectrostatic binding for both isomers occurs in the minor groove. Analogous distamycin studies with Cr(phen)(3)(3+) are als o in accord with minor groove binding.